Surface wave magnitude was initially developed in the 1950s by the same researchers who developed the local magnitude scale ML in order to improve resolution on larger earthquakes:[2]

The successful development of the local-magnitude scale encouraged Gutenberg and Richter to develop magnitude scales based on teleseismic observations of earthquakes. Two scales were developed, one based on surface waves, Ms{\displaystyle M_{s}}, and one on body waves, Mb{\displaystyle M_{b}}.
Surface waves with a period near 20 s generally produce the largest amplitudes on a standard long-period seismograph, and so the amplitude of these waves is used to determine Ms{\displaystyle M_{s}}, using an equation similar to that used for ML{\displaystyle M_{L}}.